1. Field of the Invention
The present invention relates to a numerical control processor, called herein NC processor, with an onboard grinding unit, in which a workpiece held on a work spindle is cut or machined by a Y-axis tool moved in and out with high-speed and high-acceleration in synchronized relation with a turning of the spindle, followed by being polished or finished by the grinding unit.
2. Description of the Prior Art
There is conventionally known a lathe with an onboard grinding machine, in which a workpiece cut into a desired form can be introduced to grinding operation intact without removed from chucks on a spindle of the lathe. In Japanese Patent Laid-Open No. 7-276104, there is disclosed an example of the prior lathe with onboard grinding machine, in which a cross slide is mounted on a reciprocating carriage that is installed on a machine bed of a lathe with a feed control. A tool rest is placed on this side of a horizontal top surface of the cross slider while a motor-driven grinding wheel is placed on the far side of the horizontal top surface of the cross slider. The grinding wheel is supported on a pedestal that is fixed at a horizontal bottom thereof to the horizontal top surface of the cross slider in a way keeping an axis of the grinding wheel parallel and virtually flush with an axis of a spindle.
Moreover, there is also known an attachment used in turret lathes to allow the composite processing lathes to perform a imperfect circular machining or eccentric machining with high efficiency and high precision without making a sacrifice of specific function in the composite processing lathes. Japanese Patent Laid-Open No. 8-57702, for example, discloses the attachment of the sort stated just earlier. The prior attachment to make the imperfect circular contour and eccentric contour is fastened to any one of turning tool stations on a turret tool holder of the composite processing lathe and indexed for up to machining position where a clutch jaw on a driving shaft end in the tool holder makes engagement with another clutch jaw on a driven shaft end of the attachment. With the composite processing lathe constructed as stated earlier, a servomotor in the tool holder using NC drive to control the turning position of cutting tool actuates a rotating shaft through a rack-and-pinion drive to move the tool holder along an X-axis linear guide way, providing accurate X-axis position control relative to a turning angle of a spindle through synchronous control of a spindle motor with a rotating shaft motor to perform the imperfect circular machining or eccentric machining.
A process for producing an asymmetrically centered, aspheric surface with accuracy and very short time, using NC processors is known to those skilled in the art. The prior process is disclosed, for example in Japanese Patent Laid-Open No. 11-309602, in which a Z-axis table having a headstock thereon is kept against movement while on a processing operation. A workpiece is mounted in a chuck on the headstock to be driven with a spindle motor, while a slider having a cutting tool thereon moves in and out in a Z-axis direction under NC control. Moreover, an X-axis table supporting the slider thereon travels in a reciprocating manner in the Z-axis direction. Thus, the slider and the X-axis table are allowed to reciprocate with one another in synchronized relation with the turning of the workpiece.
The recent NC processors are designed to shape any end face and an external diameter of a workpiece into a desired complex contour with three machine axes: a turning axis of a spindle, an X-axis and a Y-axis. Programming for turning the workpiece consists of an incremental amount of movement in a specific period of time. The program for the numerical control is fed to the NC processor from any external personal computer via a high-speed bus to perform direct numerical control (DNC) operation, which performs automatic operation while on read-in of the programs through an interface. According to the DNC operation, the read-in programs may be selected and the computer numerical control (CNC) is performed while on determining the execution sequence and times of the programs. Moreover, the advanced NC processors have learning functions on the X- and Y-axes, and can be controlled for even the Z-axis in the same way as to the X- and Y-axes.
Meanwhile, the present applicant has developed the NC processor of the sort shown in FIG. 4, which is disclosed in, for example Japanese Patent Laid-Open No. 2003-94204. The NC processor is envisaged to machine a plurality of works 9A including lenses, and so on at the same time. The NC processor is comprised of a work spindle 10 driven with a spindle motor 7 and supported for rotation on a headstock 5 arranged above a machine bed 2, a chuck 8 clamping a jig block 17 in a relation that a turning axis thereof is in axial alignment with a turning axis of the work spindle 10, works 9A fastened to the jig block 17 in a way positioned circumferentially at regular intervals around the turning axis of the jig block 17, a Z-axis table 3 supporting the headstock 5 thereon and getting moved in and out with a servomotor 6 in a Z-axis direction along the turning axis of the work spindle 10, an X-axis table 4 moved in a reciprocating manner with a servomotor 19 in an X-axis direction that intersects with the Z-axis direction at right angles, a sliding base 1 and tool rests 23 installed on the X-axis table 4 in opposition to the headstock 10, various X-axis cutting tools 24 mounted on the tool rest 23, a slide block 16 fastened to sliding base 1, a slider 18 having a Y-axis cutting tool 20 moved in a reciprocating manner over the slide block 16 in a Y-axis direction that intersects with the Y-axis direction at right angles, and driving means forcing the slider 18 to move in and out in a synchronized relation with a turning of the work spindle 10.
With the NC processor constructed as stated just earlier, the Y-axis cutting tool 20 is used directly upon the work 9A to machine sequentially it into a desired contour, as the slider 18 is moved in and out in the Y-axis direction in synchronized relation with the turning of the work spindle 10 in compliance with a preselected profile expected to generate sequentially on the work set up on the jig block 17. Moreover, the slider 18 is driven to move in and out with a linear motor, which is composed of magnetic windings and field magnets allowed to move relatively to the magnetic windings, either of the magnetic windings and the field magnets being installed in the slider 18 and the other in the slide block 16.
In the prior NC processor, the cutting tool to turn the workpiece is usually made of a diamond of single crystal, a tool nose radius R of which is ground below a specific tolerance.
With the prior NC processor to finish the work of transparent resin for optical purposes, nevertheless, any machine marks or traces caused by cutting tool remains on the processed surface of the work even after the completion of the cutting operation, thereby resulting in taking away commercial value from the products. To deal with this issue as stated earlier, the products have to be post-treated of attempting to grind the machined surface of the work to produce a high-quality surface finish on the workpiece.
In the conventional processors of the sort stated earlier, accordingly, the workpiece commonly is first machined to generate a desired profile or contour thereon and then subject to the surface finishing process to remove any scratches and machine marks from the machined surface of the workpiece. Generally, the profile generating process and the surface finishing process are performed, using respective special-purpose machines. This is because two categories of first process for generating any desired contour on the work and the second process or honing process for removing any roughness from the machined surface of the workpiece are distinct in processing technique from one another and therefore can not be realized by only a single processor. Thus, the workpiece has to be removed from the profile generating machine after the completion of the profile generating process and then set on the surface finisher. Handling the workpiece between the distinct processors has caused decreasing the available percentage of the finished product.
Moreover, the workpiece cut into any desired contour has to be reset on another processor. To do this, the workpiece is needed to go through some troublesome process of attempting to get the centre of the workpiece to align accurately with the turning axis of the processor. This reset of the workpiece to the processor would result in raising the percent defective of the products. That is to say, it is almost impossible to align the contour on the workpiece throughout both the preceding process for generating any desired contour on the workpiece and succeeding process to produce the high-quality surface finish. To cope with this, the second process of honing operation is needed to remove a relatively much amount of substance, including a margin of error that would occur due to the reset of the workpiece, from machined surface of the workpiece. This means it would take plenty of time to finish a workpiece while there would be inevitable some discrepancy between the preselected contour and the finished one. This discrepancy could cause any inferior products that are out of conformity to the original design specifications, reducing the available percentage of the finished products.